Differential Immune Response to Bioprosthetic Heart Valve Tissues in the α1,3Galactosyltransferase-Knockout Mouse Model

Structural valve deterioration (SVD) of bioprosthetic heart valves (BHVs) has great clinical and economic consequences. Notably, immunity against BHVs plays a major role in SVD, especially when implanted in young and middle-aged patients. However, the complex pathogenesis of SVD remains to be fully characterized, and analyses of commercial BHVs in standardized-preclinical settings are needed for further advancement. Here, we studied the immune response to commercial BHV tissue of bovine, porcine, and equine origin after subcutaneous implantation into adult α1,3-galactosyltransferase-knockout (Gal KO) mice. The levels of serum anti-galactose α1,3-galactose (Gal) and -non-Gal IgM and IgG antibodies were determined up to 2 months post-implantation. Based on histological analyses, all BHV tissues studied triggered distinct infiltrating cellular immune responses that related to tissue degeneration. Increased anti-Gal antibody levels were found in serum after ATS 3f and Freedom/Solo implantation but not for Crown or Hancock II grafts. Overall, there were no correlations between cellular-immunity scores and post-implantation antibodies, suggesting these are independent factors differentially affecting the outcome of distinct commercial BHVs. These findings provide further insights into the understanding of SVD immunopathogenesis and highlight the need to evaluate immune responses as a confounding factor.

α-Gal antigen-deficient rabbits with GGTA1 gene disruption via CRISPR/Cas9

BACKGROUND

Previous studies have identified the carbohydrate epitope Galα1-3Galβ1-4GlcNAc-R (termed the α-galactosyl epitope), known as the α-Gal antigen as the primary xenoantigen recognized by the human immune system. The α-Gal antigen is regulated by galactosyltransferase (GGTA1), and α-Gal antigen-deficient mice have been widely used in xenoimmunological studies, as well as for the immunogenic risk evaluation of animal-derived medical devices. The objective of this study was to develop α-Gal antigen-deficient rabbits by GGTA1 gene editing with the CRISPR/Cas9 system.

RESULTS

The mutation efficiency of GGTA1 gene-editing in rabbits was as high as 92.3% in F0 pups. Phenotype analysis showed that the α-Gal antigen expression in the major organs of F0 rabbits was decreased by more than 99.96% compared with that in wild-type (WT) rabbits, and the specific anti-Gal IgG and IgM antibody levels in F1 rabbits increased with increasing age, peaking at approximately 5 or 6 months. Further study showed that GGTA1 gene expression in F2-edited rabbits was dramatically reduced compared to that in WT rabbits.

CONCLUSIONS

α-Gal antigen-deficient rabbits were successfully generated by GGTA1 gene editing via the CRISPR/Cas9 system in this study. The feasibility of using these α-Gal antigen-deficient rabbits for the in situ implantation and residual immunogenic risk evaluation of animal tissue-derived medical devices was also preliminarily confirmed.

Mechanisms and Drug Therapies of Bioprosthetic Heart Valve Calcification

Valve replacement is the main therapy for valvular heart disease, in which a diseased valve is replaced by mechanical heart valve (MHV) or bioprosthetic heart valve (BHV). Since the 2000s, BHV surpassed MHV as the leading option of prosthetic valve substitute because of its excellent hemocompatible and hemodynamic properties. However, BHV is apt to structural valve degeneration (SVD), resulting in limited durability. Calcification is the most frequent presentation and the core pathophysiological process of SVD. Understanding the basic mechanisms of BHV calcification is an essential prerequisite to address the limited-durability issues. In this narrative review, we provide a comprehensive summary about the mechanisms of BHV calcification on 1) composition and site of calcifications; 2) material-associated mechanisms; 3) host-associated mechanisms, including immune response and foreign body reaction, oxidative stress, metabolic disorder, and thrombosis. Strategies that target these mechanisms may be explored for novel drug therapy to prevent or delay BHV calcification.

The role of antibody responses against glycans in bioprosthetic heart valve calcification and deterioration

Bioprosthetic heart valves (BHVs) are commonly used to replace severely diseased heart valves but their susceptibility to structural valve degeneration (SVD) limits their use in young patients. We hypothesized that antibodies against immunogenic glycans present on BHVs, particularly antibodies against the xenoantigens galactose-α1,3-galactose (αGal) and N-glycolylneuraminic acid (Neu5Gc), could mediate their deterioration through calcification. We established a large longitudinal prospective international cohort of patients (n = 1668, 34 ± 43 months of follow-up (0.1–182); 4,998 blood samples) to investigate the hemodynamics and immune responses associated with BHVs up to 15 years after aortic valve replacement. Early signs of SVD appeared in <5% of BHV recipients within 2 years. The levels of both anti-αGal and anti-Neu5Gc IgGs significantly increased one month after BHV implantation. The levels of these IgGs declined thereafter but anti-αGal IgG levels declined significantly faster in control patients compared to BHV recipients. Neu5Gc, anti-Neu5Gc IgG and complement deposition were found in calcified BHVs at much higher levels than in calcified native aortic valves. Moreover, in mice, anti-Neu5Gc antibodies were unable to promote calcium deposition on subcutaneously implanted BHV tissue engineered to lack αGal and Neu5Gc antigens. These results indicate that BHVs manufactured using donor tissues deficient in αGal and Neu5Gc could be less prone to immune-mediated deterioration and have improved durability.

In a large cohort of patients who underwent aortic valve replacement, antibody responses to glycans present in bioprosthetic heart valves, notably galactose-α1,3-galactose and N-glycolylneuraminic acid, were implicated in valve calcification and deterioration.

Calcium-Dependent Cytosolic Phospholipase A2α as Key Factor in Calcification of Subdermally Implanted Aortic Valve Leaflets

Calcium-dependent cytosolic phospholipase A2α (cPLA2α) had been previously found to be overexpressed by aortic valve interstitial cells (AVICs) subjected to in vitro calcific induction. Here, cPLA2α expression was immunohistochemically assayed in porcine aortic valve leaflets (iAVLs) that had undergone accelerated calcification subsequent to 2- to 28-day-long implantation in rat subcutis. A time-dependent increase in cPLA2α-positive AVICs paralleled mineralization progression depending on dramatic cell membrane degeneration with the release of hydroxyapatite-nucleating acidic lipid material, as revealed by immunogold particles decorating organelle membranes in 2d-iAVLs, as well as membrane-derived lipid byproducts in 7d- to 28d-iAVLs. Additional positivity was detected for (i) pro-inflammatory IL-6, mostly exhibited by rat peri-implant cells surrounding 14d- and 28d-iAVLs; (ii) calcium-binding osteopontin, with time-dependent increase and no ossification occurrence; (iii) anti-calcific fetuin-A, mostly restricted to blood plasma within vessels irrorating the connective envelopes of 28d-iAVLs; (iv) early apoptosis marker annexin-V, limited to sporadic AVICs in all iAVLs. No positivity was found for either apoptosis executioner cleaved caspase-3 or autophagy marker MAP1. In conclusion, cPLA2α appears to be a factor characterizing AVL calcification concurrently with a distinct still uncoded cell death form also in an animal model, as well as a putative target for the prevention and treatment of calcific valve diseases.

Immunological Risk Assessment of Xenogeneic Dural Patch by Comparing with Raw Material via GTKO Mice

OBJECTIVE

In this study, α-Gal epitope-deficient (GGTA1 knockout (GTKO)) mice were used to assess the immunological risks of xenogeneic dural patch by comparing with raw material.

METHODS

The xenogeneic dural patch (T2) was prepared from bovine pericardium (T1, raw material) through decellularization and carboxymethyl chitosan (CMCS) coating. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the collagen fibers and surface microstructural changes in the T1 and T2 samples. The remnant α-Gal epitopes and DNA of implants were detected by standardized method. T1 and T2 were implanted subcutaneously into GTKO mice for 4 and 12 weeks, respectively, and the negative control group (Con) was only performed sham operation. The total serum antibody, anti-Gal antibody, and splenic lymphocyte subtypes were analyzed by ELISA or flow cytometry, and histological analysis of implant-tissue was performed by H&E and Masson stain.

RESULTS

TEM and Sirius red staining showed that the collagen fibers in the dural patch were closely arranged, and SEM showed that a loose three-dimensional structure was successfully constructed on the surface of the dural patch after CMCS coating. The remnant DNA in T2 was 24.64 ± 8.73 ng/mg (dry weight), and clearance of α-Gal epitope was up to 99.83% compared to T1. The significant increases in serum total IgM, anti-Gal IgG, and anti-Gal IgM at 4 weeks and the significant changes in anti-Gal IgG and spleen lymphocyte at 12 weeks were observed in the T1 group, but no significant change was observed in the T2 group, compared to the control group. Histological semiquantitative analysis showed severe cell and tissue responses at 4 weeks and a moderate response at 12 weeks in the T1 group, while a moderate response at 4 weeks and a slight response at 12 weeks in the T2 group.

CONCLUSIONS

The results demonstrated that the xenogeneic dural patch has a lower and acceptable immunological risk compared to the raw material and control, respectively. On the other hand, it was suggested that GTKO mice are useful experimental model for immunological risk assessment of animal tissue-derived biomaterials.

Models of immunogenicity in preclinical assessment of tissue engineered heart valves

Tissue engineered heart valves may one day offer an exciting alternative to traditional valve prostheses. Methods of construction vary, from decellularised animal tissue to synthetic hydrogels, but the goal is the same: the creation of a 'living valve' populated with autologous cells that may persist indefinitely upon implantation. Previous failed attempts in humans have highlighted the difficulty in predicting how a novel heart valve will perform in vivo. A significant hurdle in bringing these prostheses to market is understanding the immune reaction in the short and long term. With respect to innate immunity, the chronic remodelling of a tissue engineered implant by macrophages remains poorly understood. Also unclear are the mechanisms behind unknown antigens and their effect on the adaptive immune system. No silver bullet exists, rather researchers must draw upon a number of in vitro and in vivo models to fully elucidate the effect a host will exert on the graft. This review details the methods by which the immunogenicity of tissue engineered heart valves may be investigated and reveals areas that would benefit from more research. STATEMENT OF SIGNIFICANCE: Both academic and private institutions around the world are committed to the creation of a valve prosthesis that will perform safely upon implantation. To date, however, no truly non-immunogenic valves have emerged. This review highlights the importance of preclinical immunogenicity assessment, and summarizes the available techniques used in vitro and in vivo to elucidate the immune response. To the authors knowledge, this is the first review that details the immune testing regimen specific to a TEHV candidate.

Specificity profile of αGal antibodies in αGalT KO mice as probed with comprehensive printed glycan array: Comparison with human anti-Galili antibodies

BACKGROUND

The α1,3-galactosyltransferase gene-knockout (GalT KO) mice are able to produce natural anti-αGal antibodies apparently without any specific immunization. GalT KO mice are commonly used as a model immunological system for studying anti-αGal responses to Gal-positive xenografts in human. In this study, we compared the specificity of mouse and human αGal antibodies to realize the adequacy of the murine model.

METHODS

Using hapten-specific affinity chromatography antibodies against Galα1-3Galβ1-4GlcNAcβ epitope were isolated from both human and GalT KO mice blood sera. Specificity of isolated antibodies was determined using a printed glycan array (PGA) containing 400 mammalian glycans and 200 bacterial polysaccharides.

RESULTS

The quantity of isolated specific anti-Galα antibodies corresponds to a content of <0.2% of total Ig, which is an order of magnitude lower than that generally assumed for both human and murine peripheral blood immunoglobulin, with a high predominance of IgM over IgG (95% vs 5%). Analysis using a printed glycan array has demonstrated that (a) antibodies from both species bind not only the Galα1-3Galβ1-4GlcNAcβ epitope, but also unrelated glycans; (b) particularly, for human (but not mouse) antibodies the best binders appear to be bacterial polysaccharides; (c) the profile of mouse antibodies is broader, it is noteworthy that they recognize a variety of human blood group B epitopes and even glycans without the α-galactosyl residue.

CONCLUSIONS

We believe that the mouse model should be used cautiously in xenotransplantation experiments when the fine epitope specificity of antibodies is critical.

Perigraft reaction and incorporation of porcine and bovine pericardial patches

OBJECTIVES

Bovine and porcine pericardial patches are frequently used in cardiothoracic and vascular surgery. There are no guidelines recommending the usage of these patches for particular surgical approaches. However, these 2 materials supposedly possess different properties. The clinical advantage of porcine compared with bovine patches remains controversial. In this experimental study, we analysed the incorporation and vascularization of bovine and porcine pericardial patches during the initial phase after implantation.

METHODS

Bovine and porcine pericardial patches were implanted into the dorsal skinfold chamber of C57BL/6 mice (n = 8 per group) to study vascularization and inflammation at the implantation site using repetitive intravital fluorescence microscopy over a 14-day period. At the end of the in vivo experiments, CD-31-positive cells were determined to evaluate the vascularization by immunohistochemistry. Furthermore, cell proliferation and apoptosis were analysed immunohistochemically.

RESULTS

Implanted bovine patches exhibited an enhanced vascularization, as indicated by a significantly higher number of CD-31-positive cells and micro-vessels (23.2 ± 4.3 vs 16.5 ± 5.8 mm-2; P = 0.001). Furthermore, bovine patches showed a slightly but not significantly higher functional capillary density. Both patches induced a moderate leukocytic inflammatory host tissue response, and neither bovine nor porcine patches significantly affected apoptosis and cell proliferation at the implantation site.

CONCLUSIONS

Bovine and porcine pericardial patches are similarly suitable for surgery. Bovine patches exhibited an improved vascularization during the first 14 days after implantation. This may result in a quicker and improved incorporation into the surrounding tissue compared with porcine pericardial patches.

A preclinical trial of perventricular pulmonary valve implantation: Pericardial versus aortic porcine valves mounted on self-expandable stent

Perventricular pulmonary valve implantation (PPVI) of a xenograft valve can be a less invasive technique that avoids cardiopulmonary bypass in patients who require pulmonary valve replacement. We compared the hemodynamics, durability, and histologic changes between two different xenogenic valves (pericardial vs. aortic valve porcine xenografts) implanted into the pulmonary valve position using a PPVI technique and evaluated the safety and efficacy of PPVI as a preclinical study. In 18 sheep, pericardial (group porcine pericardial [PP], n = 9) or aortic valve (group porcine aortic valve [PAV], n = 9) xenogenic porcine valves manufactured as a stented valve were implanted using a PPVI technique. The porcine tissues were decellularized, alpha-galactosidase treated, fixed with glutaraldehyde after space-filler treatment, and detoxified to improve durability. Hemodynamic and immunohistochemical studies were performed after the implantation; radiologic and histologic studies were performed after a terminal procedure. All stented valves were positioned properly after the implantation, and echocardiography and cardiac catheterization demonstrated good hemodynamic state and function of the valves. All the anti-α-Gal IgM and IgG titers were below 0.3 optical density. Computed tomography of extracted valves demonstrated no significant differences in the degree of calcification between the two groups (P = .927). Microscopic findings revealed a minimal amount of calcification and no significant infiltration of macrophage or T-cell in both groups, regardless of the implantation duration. The PPVI is a feasible technique. Both stented valves made of PP and PAV showed no significant differences in hemodynamic profile, midterm durability, and degree of degenerative dystrophic calcification.

Studying Xenograft Rejection of Bioprosthetic Heart Valves

Millions of patients with valvular heart disease have benefitted from heart valve replacement since the procedure was first introduced in the 1960s; however, there are still many patients who get early structural valve deterioration (SVD) of their bioprosthetic heart valves (BHV). BHV are porcine, bovine, or equine tissues that have been glutaraldehyde fixed to preserve the tissue and presumably make the tissue immunologically inert. These glutaraldehyde-fixed BHV with anti-calcification treatments last long periods of time in older adults but develop early SVD in younger patients. The consensus at present is that the early SVD in younger patients is due to more "wear and tear" of the valves and higher calcium turnover in younger patients. However, as younger patients likely have a more robust immune system than older adults, there is a new hypothesis that BHV xenografts may undergo xenograft rejection, and this may contribute to the early SVD seen in younger patients.At present, the technology to noninvasively study in vivo whether an implanted BHV in a human patient is undergoing rejection is not available. Thus, a small animal discordant xenotransplant model in young rodents (to match the young patient getting a pig/bovine/equine BHV) was developed to study whether the hypothesis that glutaraldehyde-fixed BHV undergo xenograft rejection had any merit. In this chapter, we describe our model and its merits and the results of our investigations. Our work provides clear evidence of xenograft rejection in glutaraldehyde-fixed tissue, and our small animal model offers an opportunity to study this process in detail.

Xenogeneic bone matrix immune risk assessment using GGTA1 knockout mice

Homeotransplantation of bones for replacement therapy have been demonstrated reliably in clinical data. However, human donor bones applicable for homeotransplantation are in short supply, which facilitates the search for suitable alternatives, such as xenografts grafts. The α-Gal antigen-related immune risk of xenografts directly affects the safety and effectiveness of the biomaterials and limits their applications in the clinic. The immune risk can be prevented by depletion or breaking anti-Gal antibody prior to transplant. Therefore, how to assess the immune risk of the bone substitutes and select the reliable animal research model become extremely important. In this study, we prepared lyophilized bone substitutes (T1) and Guanghao Biotech bone substitutes (T2, animal-derived biomaterials with α-Gal antigen decreased), aimed to assess the immune risk of xenografts bone substitutes on GGTA1 knockout mice. The α-Gal antigen contents of T1 and T2 were firstly detected by ELISA method in vitro. The bone substitutes were then implanted subcutaneously into GGTA1 knockout mice for 2, 4 and 12 weeks, respectively. The total serum antibody levels, anti-α-Gal antibody levels, inflammatory cytokine and splenic lymphocyte surface molecules were detected and histology analysis of skin and thymus were performed to systematically evaluate the immune response caused by the T1 and T2 bone substitutes in mice. In vitro results showed that the amount of α-Gal epitopes in T1 bone substitutes was significantly higher than T2 bone substitutes, and the clearance rate of α-Gal antigen in T2 bone substitutes achieved about 55.6%. Results of antibody level in vivo showed that the T1 bone substitutes group possessed significantly higher total IgG, IgM, IgA and anti-α-Gal IgG levels than T2 and control group, while T2 group showed no significant changes of these indexes compared with control. In terms of inflammatory cytokines, T1 bone substitutes showed evidently higher levels of IL-4, IL-12P70 and IL-10 than T2 and control, while T2 group was comparable to control. No changes in the levels of splenic lymphocyte surface molecules were found in the three groups (T1, T2 and control group) during the experimental periods. The pathological results demonstrated that the inflammatory response in T2 group was lighter than the T1 group, which was in accordance with the inflammatory cytokines levels. The above results indicated that the process of antigen removal effectively reduced the α-Gal antigens content in T2 bone substitutes, which caused little immune response in vivo and could be used as bone healing materials. This study also demonstrated that GGTA1 knockout mice can be used as a routine tool to assess the immune risk of animal-derived biomaterials.

Effects of antigen removal on a porcine osteochondral xenograft for articular cartilage repair

Given the limited availability of fresh osteochondral allografts and uncertainty regarding performance of decellularized allografts, this study was undertaken as part of an effort to develop an osteochondral xenograft for articular cartilage repair. The purpose was to evaluate a simple antigen removal procedure based mainly on treatment with SDS and nucleases. Histology demonstrated a preservation of collagenous structure and removal of most nuclei. Immunohistochemistry revealed the apparent retention of α-Gal within osteocyte lacunae unless the tissue underwent an additional α-galactosidase processing step. Cytoplasmic protein was completely removed as shown by Western blot. Quantitatively, the antigen removal protocol was found to extract approximately 90% of DNA from cartilage and bone, and it extracted over 80% of glycosaminoglycan from cartilage. Collagen content was not affected. Mechanical testing of cartilage and bone were performed separately, in addition to testing the cartilage-bone interface, and the main effect of antigen removal was an increase in cartilage hydraulic permeability. In vivo immunogenicity was assessed by subcutaneous implantation into DBA/1 J mice, and the response was typical of a foreign body rather than immune reaction. Thus, an osteochondral xenograft produced as described has the potential for further development into a treatment for osteochondral lesions in the human knee. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2251-2260, 2018.

Congenital aortic valve repair using CorMatrix® : A histologic evaluation

BACKGROUND

The reconstruction of heart valves provides substantial benefits, particularly in the pediatric population. We present our experience using decellularized extracellular matrix (dECM, CorMatrix^® ) for aortic valve procedures.

METHODS

We retrospectively reviewed the case histories of 6 patients (aged from 2 months - 14 years) who underwent surgery for severe aortic valve stenosis (n = 4) or regurgitation (n = 2). Aortic valve repair was performed on all patients using dECM as a leaflet replacement or leaflet extension. Follow-ups were performed using echocardiography. Reoperation was necessary in 4 cases, and the dECM was explanted and examined histologically and immunohistochemically.

RESULTS

The early post-operative period was uneventful, and the scaffold fulfilled the mechanical requirements. Significant valve insufficiency developed in 5 patients during the post-operative period (119-441 days postoperatively). In all specimens, only a migration of inflammatory cells was identified, which induced structural and functional changes caused by the chronic inflammatory response.

CONCLUSIONS

Our results suggest a mixed immunological response of remodeling and inflammation following the implantation. The expected process of seeding/migration and remodeling of the bioscaffold into the typical 3-layered architecture were not observed in our explanted specimens.

Effects of glutaraldehyde concentration and fixation time on material characteristics and calcification of bovine pericardium: implications for the optimal method of fixation of autologous pericardium used for cardiovascular surgery

Objectives

Autologous pericardium, which is widely used in the field of cardiovascular surgery, is usually fixed with glutaraldehyde (GA) to improve handling and provide biomechanical stability. However, an optimal method of GA fixation of autologous pericardium is not known. The objective of this study was to evaluate the effects of GA concentration and fixation time on material characteristics and calcification of bovine pericardium.

Methods

Bovine pericardial tissues were fixed with different concentrations of GA (0.3, 0.4, 0.5 and 0.6%) for different exposure times (10 and 20 min). Material characteristics of the fixed tissues were assessed by mechanical test, thermal stability test and pronase test. The tissues were subcutaneously implanted into 3-week-old rats for 2 months, and the calcium contents of the explanted tissues were measured. Differences between the groups were evaluated by two-way analysis of variance.

Results

Differently treated tissues showed no significant differences in tensile strength. The mean elongation at break of the pericardial tissues fixed with 0.5 and 0.6% was significantly higher compared with 0.3 and 0.4% when fixed for 20 min. The mean elongation at break of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min when fixed with 0.5 and 0.6%. Thermal stability test revealed significantly higher mean shrinkage temperature of the pericardial tissues fixed with 0.6% compared with lower concentrations irrespective of fixation time. The mean shrinkage temperature of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min irrespective of GA concentration. Pronase test revealed significantly lower mean percent remaining weight of the pericardial tissues fixed with 0.3% compared with higher concentrations irrespective of fixation time. The mean percent remaining weight of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min irrespective of GA concentration. The mean calcium content of the pericardial tissues fixed with 0.6% was significantly lower than that of the pericardial tissues fixed with 0.4% irrespective of fixation time.

Conclusions

Fixation of bovine pericardium with 0.5 and 0.6% GA for 20 min produced superior results with regard to material characteristics (mechanical properties, degree of fixation and resistance to enzymatic degradation) and postimplantation calcification. These results may have implications for optimal fixation of autologous pericardium used for cardiovascular surgery.

Comparative Decellularization and Recellularization of Wild-Type and Alpha 1,3 Galactosyltransferase Knockout Pig Lungs: A Model for Ex Vivo Xenogeneic Lung Bioengineering and Transplantation

BACKGROUND

A novel potential approach for lung transplantation could be to utilize xenogeneic decellularized pig lung scaffolds that are recellularized with human lung cells. However, pig tissues express several immunogenic proteins, notably galactosylated cell surface glycoproteins resulting from alpha 1,3 galactosyltransferase (α-gal) activity, that could conceivably prevent effective use. Use of lungs from α-gal knock out (α-gal KO) pigs presents a potential alternative and thus comparative de- and recellularization of wild-type and α-gal KO pig lungs was assessed.

METHODS

Decellularized lungs were compared by histologic, immunohistochemical, and mass spectrometric techniques. Recellularization was assessed following compartmental inoculation of human lung bronchial epithelial cells, human lung fibroblasts, human bone marrow-derived mesenchymal stromal cells (all via airway inoculation), and human pulmonary vascular endothelial cells (CBF) (vascular inoculation).

RESULTS

No obvious differences in histologic structure was observed but an approximate 25% difference in retention of residual proteins was determined between decellularized wild-type and α-gal KO pig lungs, including retention of α-galactosylated epitopes in acellular wild-type pig lungs. However, robust initial recellularization and subsequent growth and proliferation was observed for all cell types with no obvious differences between cells seeded into wild-type versus α-gal KO lungs.

CONCLUSION

These proof of concept studies demonstrate that decellularized wild-type and α-gal KO pig lungs can be comparably decellularized and comparably support initial growth of human lung cells, despite some differences in retained proteins. α-Gal KO pig lungs are a suitable platform for further studies of xenogeneic lung regeneration.

In vivo xenogeneic scaffold fate is determined by residual antigenicity and extracellular matrix preservation

The immunological potential of animal-derived tissues and organs is the critical hurdle to increasing their clinical implementation. Glutaraldehyde-fixation cross-links proteins in xenogeneic tissues (e.g., bovine pericardium) to delay immune rejection, but also compromises the regenerative potential of the resultant biomaterial. Unfixed xenogeneic biomaterials in which xenoantigenicity has been ameliorated and native extracellular matrix (ECM) architecture has been maintained have the potential to overcome limitations of current clinically utilized glutaraldehyde-fixed biomaterials. The objective of this work was to determine how residual antigenicity and ECM architecture preservation modulate recipient immune and regenerative responses towards unfixed bovine pericardium (BP) ECM scaffolds. Disruption of ECM architecture during scaffold generation, with either SDS-decellularization or glutaraldehyde-fixation, stimulated recipient foreign body response and resultant fibrotic encapsulation following leporine subpannicular implantation. Conversely, BP scaffolds subjected to stepwise removal of hydrophilic and lipophilic antigens using amidosulfobetaine-14 (ASB-14) maintained native ECM architecture and thereby avoided fibrotic encapsulation. Removal of hydrophilic and lipophilic antigens significantly decreased local and systemic graft-specific, adaptive immune responses and subsequent calcification of BP scaffolds compared to scaffolds undergoing hydrophile removal only. Critically, removal of antigenic components and preservation of ECM architecture with ASB-14 promoted full-thickness recipient non-immune cellular repopulation of the BP scaffold. Further, unlike clinically utilized fixed BP, ASB-14-treated scaffolds fostered rapid intimal and medial vessel wall regeneration in a porcine carotid patch angioplasty model. This work highlights the importance of residual antigenicity and ECM architecture preservation in modulating recipient immune and regenerative responses towards xenogeneic biomaterial generation.